Friday, August 7, 2009

This tutorial will help you turn your Windows based system into a SecureFTP server.

BackgroundSecure Shell (SSH) is a program that lets you log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another. It provides strong authentication and secure communications over insecure channels. When using ssh, the entire login session, including transmission of password, is encrypted and therefore is very secure.

You may have noticed that many webhosts allow ssh access. This means that you can login to their webserver and execute many UNIX commands (the ones they allow you access to) on your account. Not only can you connect to other computers that provide SSH access, but you can also allow others to connect to your computer using SSH.

To take this one step further, you can also turn your Windows PC into a Secure FTP (SFTP) server. SFTP is a program that uses SSH to transfer files. Unlike standard FTP, it encrypts both commands and data, preventing passwords and sensitive information from being transmitted in clear text over the Internet. It is similar to FTP, but because it uses a different protocol, you must use a FTP client that supports SFTP (more about that later).

Installing SSH on WindowsMost UNIX based systems (Linux and OSX) come with SSH preinstalled, so connecting to a remote host is very easy. However, if you run a Windows system, you need to download some additional software to make the SSH programs available to you. Fortunately a free open-source project called SSHWindows, provides a nice Windows installer that will setup the SSH client and Server on your system.

Configure the SSH ServerIn this next step, I have summarized the information that is included with the readme.txt that is included with SSHWindows (it can be found in c:\program files\openssh\docs)Your first configuration step is to set up the passwd file. You will need to set up the passwd file before any logins can take place.

Passwd creation is relatively easy and can be done using two programs that are included with SSHWindows – mkgroup and mkpasswd. Both of these programs are located in the c:\program files\openssh\bin directory.

To begin creating the group and passwd files, open a command prompt window and navigate to the c:\program files\openssh directory.

You must first create a group file. To add all local groups on your computer to the group file, type the command as shown below:

mkgroup -l >> ..\etc\group

You will now need to create a passwd file. Any users in the passwd file will be able to log on with SSH. For this reason, it is recommended that you add users individually with the -u switch. To add a user to the passwd file type the command shown below:

mkpasswd -l -u username >> ..\etc\passwd

NOTE: the username specified above must be an existing windows login account.

Creating Home Directories for you UsersIn the passwd file, you will notice that the user’s home directory is set as /home/username, with username being the name of the account. In the default install, the /home directory is set to the default profile directory for all users. This is usually c:\documents and settings.

If you want to change this location you will need to edit the passwd file. The passwd file is in plain text and can be edited in Notepad or any text editor. The last two entries for each user are safe to edit by hand. The second to last entry (/home/username) can be replaced with any other directory to act as that user’s home directory. It’s worth noting that when you run SSH on windows, you are actually running SSH in a scaled down version of cygwin, which is a Unix emulator for Windows. So, if you will be placing the user somewhere outside the default directory for their Windows profile, you will need to use the cygdrive notation.

To access any folder on any drive letter, add /cygdrive/DRIVELETTER/ at the beginning of the folder path. As an example, to access the winnt\system32 directory on the *c:* drive you would use the path:

/cygdrive/c/winnt/system32

Connecting to your SFTP ServerTo connect to your new SFTP server, you will need to download an FTP client that supports SFTP. I use Filezilla which is a nice free FTP and SFTP client. You might also try WinSCP which is another free SFTP client.

To test if your server is running, create a new connection in your client and specify SFTP as the server type, 22 as the port, and localhost or 127.0.0.1 as the server name. You will also need to provide the user account and password for any account that you added to your passwd file. Now connect to the server. If all went well, you should see a directory listing where you pointed the home folder to. If not, there are a couple of things to check. Make sure your Windows firewall is set to allow traffic over port 22 and finally double check your passwd file to make sure that the account you added is actually there.

SecurityBecause SSH allows access to only Windows user accounts, you can restrict access based upon NTFS file permissions. As such, SFTP does not provide for chroot jails (a Unix method for locking a user to his/her home directory). Simply lock down your filesystem for that user, and SFTP will respect that.

SummaryIn the end, setting up an SFTP server turned out to be a very effortless task. With a couple of open source programs and a couple of command-line commands, you can up and running in no time at all!